The present embodiment relates generally to a method for selecting a cementing composition for sealing a subterranean zone penetrated by a well bore.
In the drilling and completion of an oil or gas well, a cementing composition is often introduced in the well bore for cementing pipe string or casing. In this process, known as “primary cementing,” a cementing composition is pumped into the annular space between the walls of the well bore and the casing. The cementing composition sets in the annular space, supporting and positioning the casing, and forming a substantially impermeable barrier, or cement sheath, which divides the well bore into subterranean zones.
If the short-term properties of the cementing composition, such as density, static gel strength, and rheology are designed as needed, the undesirable migration of fluids between zones is prevented immediately after primary cementing. However, changes in pressure or temperature in the well bore over the life of the well can compromise zonal integrity. Also, activities undertaken in the well bore, such as pressure testing, well completion operations, hydraulic fracturing, and hydrocarbon production can affect zonal integrity. Such compromised zonal isolation is often evident as cracking or plastic deformation in the cementing composition, or de-bonding between the cementing composition and either the well bore or the casing. Compromised zonal isolation affects safety and requires expensive remedial operations, which can comprise introducing a sealing composition into the well bore to reestablish a seal between the zones.
A variety of cementing compositions have been used for primary cementing. In the past, cementing compositions were selected based on relatively short term concerns, such as set times for the cement slurry. Further considerations regarding the cementing composition include that it be environmentally acceptable, mixable at the surface, non-settling under static and dynamic conditions, develop near one hundred percent placement in the annular space, resist fluid influx, and have the desired density, thickening time, fluid loss, strength development, and zero free water.
However, in addition to the above, what is needed is a method for selecting a cementing composition for sealing a subterranean zone penetrated by a well bore that focuses on relatively long term concerns, such as maintaining the integrity of the cement sheath under conditions that may be experienced during the life of the well.